This invention relates to improved means for sealing the intersection of apex and peripheral seals in rotary mechanisms. Peripheral seals disposed on the rotor of rotary mechanisms and the apex seals employed in such mechanisms generally seal well regardless of the pressure differentials thereacross. However, in the case of piston seals (frequently termed "bolts" or "buttons"), at various stages in the cyclic operation of such mechanisms, there is no ready path for fluid under pressure to be directed to the underside of the piston seal to assist in biasing the same against the wall of the chamber against which it is to seal. Consequently, the opportunity for the existence of an undesirable leakage path at each piston seal at certain points in the operation of such mechanisms exists.